A new species of Isospora Schneider (Apicomplexa: Eimeriidae) is described from captive Blue-crowned Laughingthrush Dryonastes courtoisi (Ménégaux, 1923) (Passeriformes: Timaliidae). Sporulated oocysts of Isospora courtoisii n. sp. are ellipsoidal 24.5 × 14.5 μm. Micropyle and oocyst residuum are absent. Sporocysts are broadly ellipsoidal, 15.9 × 8.5 μm, with Stieda and substieda bodies. Sporocyst residuum is scattered composed of hundreds of small granules. Sporozoites are elongate and slightly curved, each with two refractile bodies. The nuclei of the sporozoites were not well discernible. Considering the critically endangered status of Dryonastes courtoisi and assumed high host specificity of described coccidium, also I. courtoisi can be classified as critically endangered organism.
